Eph 1:4 “kathOs exelexato hEmas en autO pro katebolEs kosmou...” To begin and looking at the status of “us” we have hEmas the accusative plural. The accusative is the perfect form i.e. the complete form of named things and describe things and doing things in the participle. English has no perfect in nouns, adjectives or verbs.
The text begins kathOs which is the adverb that attributes what is about to be stated. The verb exelexato is indicative mood, aorist state, middle voice third person singular. It is found 21 times in NT Greek and always in the middle voice dominating the in the Aorist 20 times and the Imperfect only once. The middle voice changes the verbs expression and subject in NT Greek for which English has no equal translation. English translation for exelexato in the first middle active third person would be, chosen Himself.
The root of this verb is found in G1586 in Strong’s Concordance. Middle voice in NTG has six forms, middle voice; passive middle voice; middle deponent voice; passive deponent voice; middle passive voice; middle deponent passive deponent and each offers a differing nuance towards the verbs subject. The deponent middle is more imperative and emphatic than the standard middle. The passive middle or the deponent passive in any combination can not be successfully translated into English. Comparing your English bible to the text you find in this paradigm of the verb they are simply not translated.
The root verb is eklegomai is a triple construct of the preposition ek meaning out and regular verb legO meaning to lay forth. Constructing the root ek+legO+mai for the middle voice. The grammar alteration for the middle voice changers the omega (O long vowel ) of legO to omicron (o short vowel) lego then adds mai for the middle voice paradigm i.e. ek+lego+mai. There are grammar considerations for kappa (k) and Xi (x) for the preposition ek or ex.The participle retains kappa e.g eklexamenos. In other forms the kappa is altered to Xi as here in Eph 1:4. The beloved Apostle Paul had to know his grammar in order to write these words.
The other consideration for this text is the dative phrase in Him. The Latin dative is positional statement while Koiné Greek’s dative is relational speaking to a relationship as opposed to merely a position. We are not chosen in Him positional we are chosen in Him relational.
The phrase “foundation of the world” is mistranslated and should be stuck out of the English bible. The Greek phrase, pro katabolEs kosmou means “before the disruption of the system.” The reference is Gen 3 and the curse pronounced where the system is disrupted and death enters. The feminine noun first declension katabolE is the noun form of casting down. The verb form is kataballO i.e. the throw down. See Rev 12:10; 2 Cor 4:9.
Koiné Greek has no substantive where verb might do the work of noun i.e. anointed. The Greek noun names the verbal action and the verb does the work. The Greek noun for a foundation is themelois and its accompanying verb is themelioO. To speak of a foundation the noun is deployed and to make foundation the verb is used.
Hebrews 6:1 makes this idea concrete where it is stated “not laying again a foundation” i.e. mE palin thelemion. Right next to the noun foundation we have the verb kataballO applied in the passage as the participle kataballomenoi. i.e. mE palin thelemion kataballomenoi.
Because the KJV has already applied the noun foundation to katabolEs and the verb kataballO, the participle kataballomenoi was left untranslated. The translators where caught in their own conundrum. So they simple left out the participle . Hebrews 6:1 reads, “Therefore leaving aside the original doctrine of Christ the anointed on[to] maturity we should be brought [and] not again the foundation disrupting of repentance from dead works and belief on God” Repentance from dead works under the Law and a nominal belief in god is disruptive of maturity in Christ. The Hebrews were practicing this idea of always returning to the law, repenting, repenting, repenting. James also rebukes them for nominal belief and practice, "You believe in God very well even the devils believe and tremble"
Eph 1:4 speaks concerning the nations and the elect out of the nations thereof, The father chose us Himself. This choice was complete US (accusative) and in relationship with Him. This choice of Himself making us complete in Him was executed before the kosmos was disrupted in Genesis 3:15. This choice was grace alone outside of covenant and law hence the Mystery not revealed. This is the calling of the body.
Judah and Israel are called through covenant old (broken) and new (See Jer 31:31-35) This calling was from the disruption of the system. The promise made in Gen 3:15 is the seed of the women.